Useful measures for obesity medicine
How to integrate, in addition to BMI, new and useful indices for better treatment of obesity
Obesity is a disease in which fat deposits, called adiposity, are detrimental to health.
In 2024, a study published in The Lancet showed that 43 % of adults are overweight. In 2025, the director of’World Health Organization said that obesity, recognized as a chronic disease, is one of the major public health challenges worldwide. According to the WHO, an adult is considered obese when his or her body mass index (BMI) exceeds 30.
The WHO definition now incorporates new measures, as do the recommendations of Obesity Canada, to better define the disease and its real impact on health. Waist circumference, when combined with BMI, enables a more precise diagnosis. Other tools also enable us to better target the location of fat, a key determinant of health risk.
Obesity: a disease that's about more than weight
Scientific data clearly show that weight loss alone is not enough to improve health of people living with obesity. Medical management should focus on diet, avoiding restrictive diets, regular physical activity, mental health and visceral fat reduction.
Weight loss can, however, improve certain symptoms. Osteoarthritis of the knees and walking difficulties generally improve with weight reduction. In addition, about 50 % of people with sleep apnea after weight loss.
It is important to note that 29 % of obese people have normal biological and physical indicators, such as blood pressure or blood tests within the reference values.
Medical measures useful for diagnosis and follow-up
Today, several indicators are used to diagnose obesity, support weight management and monitor disease progression. These include BMI, waist circumference and waist-to-waist ratio, as well as more advanced tools such as lipodensitometry and impedancemetry.
Body mass index (BMI)
The body mass index has been around since the 1800's. It was originally developed for statistical analysis of populations and to characterize their morphology. BMI corresponds to weight in kilograms divided by height in meters squared.
A BMI greater than or equal to 25 corresponds to overweight, while a BMI greater than or equal to 30 defines obesity according to this indicator alone. Early studies showed that the higher the BMI, the greater the risk of complications. A study published in 2013 showed that people with a BMI of grade 2 or 3 have a higher risk of mortality risk more than 30 % higher compared to people with a lower BMI.
The same study suggested that overweight people could sometimes present a lower risk than those with a so-called normal BMI, possibly due to closer medical monitoring.
However, BMI should be interpreted with caution. It does not take into account the distribution between muscle mass, bone mass and fat mass. It is particularly unsuitable for athletes and short people. For example, a person measuring 1.90 m and weighing 110 kg would have a BMI of around 30, even though their muscle and bone mass account for a large proportion of their weight. BMI is therefore unable to distinguish fat weight from muscle weight, which is a major limitation to its use.
A study published in Nutrients shows that the higher the BMI, the greater the food dependency (25%) compared with those of normal weight (11%). When BMI exceeds 40, this food dependency becomes even more pronounced. The combination of high BMI and food dependency calls for greater attention in the care due to the psychological vulnerability larger.
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Waist circumference: now an essential indicator
Waist circumference measurement is now systematically added to the diagnosis of obesity. When fat deposits are concentrated in the abdominal area, health risks increase significantly. BMI alone provides no information on the distribution of fat in the body.
Abdominal obesity occurs when waist circumference exceeds 102 cm for men and 88 cm for women, outside pregnancy.
To measure waist circumference correctly, we recommend using a non-elastic tape measure, placed between the last rib of the thorax and the highest bony point of the pelvis, generally at navel level. The measurement should be taken without drawing in or inflating the belly, and ideally twice, in order to determine the average.
Waist-to-waist ratio
The ratio between waist circumference and waist circumference, expressed in the same unit of measurement, is used to assess the risk of chronic diseases associated with obesity. When this ratio exceeds 0,5, the risk of complications increases.
As an example, a person with a waist circumference of 77 cm for a height of 165 cm has a ratio of 0.46, which does not increase the risk of chronic diseases. Conversely, a waist circumference of 115 cm for a height of 175 cm corresponds to a ratio of 0.657, indicating an increased risk.
Why target visceral fat rather than weight alone
In obesity medicine, the main goal is to improve overall health and reduce the risk of complications such as cardiovascular diseases, diabetes, certain cancers, and other chronic diseases.
These improvements are primarily achieved by reducing intra-abdominal fat. When a sedentary person loses weight, this loss is generally divided into three parts: one-third of the peripheral fat layer, one-third of muscle mass, and one-third of internal fat. That is why weight remains a useful indicator, but it must always be interpreted in conjunction with the waist circumference, which more directly reflects visceral fat.
The Edmonton Stadium: assessing the severity of obesity
The Edmonton stage is a classification that allows the severity of obesity to be characterized, taking into account weight, height, comorbidities, and the stability of physical and mental health. This scale ranges from 0 to 4.
Stage 0 corresponds to a situation where obesity does not appear to harm health, while stage 4 corresponds to an unstable health situation, such as untreated diabetes, unbalanced arterial hypertension, or hyperphagic disorder associated with significant mental distress.
Body fat mass and location of body fat
In humans, a percentage of body fat between 10 and 25 % is considered normal. In women, the percentage varies generally between 20 and 35 %. Beyond these values, excess fat can become harmful, especially when it is located in the abdominal and visceral areas.
Localized fat in the lower and upper limbs is much less harmful to health than abdominal fat.
Lipodensitometry and impedancemetry
Lipodensitometry, also known as dual energy X-ray absorptiometry (DXA), allows for the precise analysis of muscle mass, bone mass and adipose mass, as well as their localization. This examination is non-invasive, painless and quick, but is currently not covered by the RAMQ. It is recommended to wear comfortable clothing, not to take calcium supplements within 24 hours before the examination and to remain immobile for a few minutes.
Impedance measurement is based on measuring the electrical resistance of the different body tissues in order to estimate the proportions of fat, muscle and water. It is also not covered by the RAMQ, except in some clinics that have impedance scales. In the Allurion program, these scales allow for precise and personalized monitoring of weight loss, distinguishing what is lost in terms of fat, muscle and water. This monitoring helps adjust dietary choices and physical activity, especially when muscle mass decreases. The contraindications of impedance measurement are pregnancy and the wearing of implanted devices such as pacemakers.
The evolution of fat with age and the role of hormones
With age, the location of body fat tends to change. In women, the approach to menopause is accompanied by a decrease in female hormones and a progressive accumulation of abdominal fat. This increase in waist circumference leads to an increase in cardiovascular risk, bringing the risk closer to that observed in men.
In men, the decrease in testosterone during andropause also promotes the accumulation of fat in the abdominal area and around the internal organs.
Muscle, body water and therapeutic objectives
One kilogram of muscle is much denser than one kilogram of fat. Muscles are rich in muscle fibers and water. The body of a man contains on average between 50 and 65 % of water, while that of a woman contains between 45 and 60 % in a normal health context.
The main medical goal is to reduce visceral and abdominal fat mass rather than focusing solely on weight. Increasing muscle mass allows the body to increase energy expenditure, promote the breakdown of visceral fat used as fuel, reduce waist circumference, and improve overall health, even when weight does not decrease significantly.
Conclusion: Going beyond the logic of the balance sheet
The management of obesity It relies on a comprehensive approach that goes far beyond simply measuring weight. The integration of BMI, waist circumference, fat distribution, comorbidities, and mental health allows for a more nuanced understanding of the disease and a lasting improvement in the health of the affected individuals. Moreover, experts like Séverine Mazur can present you with unique solutions such as the allurion gastric balloon.